Articles including electrical or electronic components such as integrated circuits, hybrid components and printed circuit boards require the deposit of a metallic film or surface coating at some point in their manufacturing process. At present the application of metallic coatings to printed circuit boards is normally performed by wet chemical processing. The processing is a continuous process however it normally involves the handling of toxic chemicals. Recently dry metallization techniques such as sputtering, vapor deposition and ion plating have been shown to satisfy coating adhesion requirements and accordingly can be utilized for practical commercial use.
In the integrated and hybrid circuit industries a variety of materials such as gold, palladium, copper, aluminum, tantalum or tantalum nitride may be deposited on ceramic or silicon substrates by a sputtering process. In the printed circuit industry copper is the typical metallic film. Once the film is deposited it can be increased in thickness, etched or otherwise fabricated into the circuits and/or components.
For a aputtering process a target of the material to be sputtered is attached to the face of the cathode. This target material is subjected to a high cathodic voltage in an inert low pressure gaseous atmosphere, such as argon, where the gas is ionized to bombard the exposed metallic surface and dislodge atoms or clusters of atoms which are subsequently deposited on the substrate.
Many dry metallization manufacturing facilities have been developed for depositing thin films of metal on substrates. In one type of continuous single line, open end apparatus the substrates are advanced through a series of individually pumped chambers of successively reduced pressure until the substrates enter a vacuum chamber where the sputtering takes place. In another type of continuous sputtering apparatus a group of substrates are advanced through a series of locks which are successively evacuated and then the substrates enter a vacuum process chamber to receive the sputter deposit. Even the sputtering of a relatively thin film takes considerable time; hence, these types of one dimensional linear facilities are necessarily slow because so few substrates are being sputtered at a time.
In batch bell jar apparatus, cylindrical arrangements of the substrates have been utilized to increase the number of substrates that are simultaneously being processed. In this arrangement substrates are positioned within a bell jar in a circular array about a centrally disposed cathode so that all substrates are simultaneously processed. This process does not lend itself to continuous operation in that the bell jar has to be sequentially vented and pumped down for each batch of processed substrates. Further, in this process, substrates can be quite large (the substrates which are used for printed circuits can be 18".times.24" or larger) and are of a planar construction. These substrates receive nonuniform deposits of metal; more being deposited in the center area of each substrate due to the closer proximity of the central area to the centrally disposed cathode.
An apparatus superior to the two previously mentioned devices in throughput and purity of the deposited film is the continuous cylindrical sputtering machine of U.S. Pat. No. 3,856,654. In this configuration the substrates are batch loaded then fed in a continuous single circular line around a centrally disposed cathode. The controlled atmosphere coating chamber is never exposed to the natural atmosphere during the coating operation which allows for a higher purity of deposit. Although the throughput of this apparatus is greater than any of the previously mentioned devices, it still operates on a one dimensional basis with a single line of substrates moving past the cathode.
While the dry metallization processes avoid the problem of toxic chemicals, they have at best limited continuous throughput capability and are most often realized in batch processing arrangements. At best when processing both sides of a substrate a single processing chamber whether continuous or batch operated can only accommodate a single throughput line.